Radiation gauges having ionization chambers



- Nov. 8; 1960 G. F. w. POWELL RADIATION GAUGES HAVING IONIZ-ATION CHAMBERS 4 Sheets-Sheet 1 Filed May 15, 1957 kW m N e Mf we Vw w w. A a W My 9 5 v\\\\\\\\ g 1AI' l I. M I! .V| y a b .L F w 9 3.5 v x a Nov. 8, 1960 e. F. w. POWELL RADIATION GAUGES HAVING IONIZATION CHAMBERS Filed May 15, 1957 4 Sheets-Sheet 2 \HHHHIHIHIHIHH lHl 'Jl Fig.2.

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RADIATION GAUGES HAVING IONIZATION CHAMBERS Filed May 15, 1957 4 Sheets-Shae; 3

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RADIATION GAUGES HAVING IONIZATION CHAMBERS Filed May 15, 1957 4 Sheets-Sheet 4 Unite rates Patent-O RADIATION GAUGES HAVING JONIZATION CHAMBERS Gordon Francis Wellington Powell, .Deptford, London,

England, assignor to Molins Machine Company Limited, LondomEngland, a British company Filed May 15, 1957, 591. No. 659,325 Claims priority, application Great Britain 'May' 15; 1956 '5 Claims. (Cl.,25033.6)

As willbe seen later, the -chamber of the pre's'ent inven- I tion is particularly useful for measuring the 'rnass -of a loose tobacco filler and'this is advantageous because the measurement can'take place at an-earlier stage '-in the manufacture of the cigarettes than when awrappeddod is measured and consequently correction of the tobacco feeding arrangements-can be made more nearly xto-the time when deviation in the mass occurs.

In ionization chambers as -hitherto-constructed,'the sensitivity can be-adjusted by altering the gas pressure in the chambenbutthis is-naturally-afairiy coarsemethod of adjustment and is not easy to-do.

According to the invention there is-prov-ided a radiation gauge for measuring ,a moving tobacco f,iller having an ionization chamber (e.g. of cylindricalshape) with a window and containing plate-like electrodes so disposed that they lie in planes transverse to theflplane of the window, and comprising means-for ;moving'(e;.-g.-rotating) the chamber whereby the electrode plates may gbe disposed in different angular relationships 'COftl'lejIZtdiO- active source of the gauge,presentingeincombination Wi h the tobacco filler which is ,interposed betweenthegsource and chamber differing. areas, or"apertures otieiramb er to the rays emitted from the source. For example the planes of the electrodes may be more or less normal to the plane of the window and cross-sections thereof parallel to the window may be parallel to one another.

The gas in the chamber which may, for example, be nitrogen, or a mixture of argon and carbon dioxide, is passed into the chamber through a metal tube permanently fixed to the chamber and when filling to the desired pressure is obtained the inlet tube is sealed so that the chamber remains permanently filled With a gas or a mixture of gases at a desired pressure.

The invention will be further described with reference to the accompanying drawings, in which:

Figure l is a section of an ionization chamber and its mounting;

Figure 2 is a transverse section of the lower part of Figure 1;

Figure 3 is a transverse section of the lower part of Figure 1 and the view is continued to show the full extent of one example of housing for the ionization chamber, said housing being shown as suitable for the chamber of a balancing unit.

Figure 4 is a diagram showing the application of the invention to the measurement of a moving tobacco filler and shows the arrangement of the scanner with respect to the trough in which the filler moves.

Figure 5 is a perspective view of the upper part of Figure 4.

introduced into .the chamber "ice 2 *Figurefi is aplan view ctr-the chamber shown in'Figure '1 with the top-removed.

Referring-toFigure 1, the chamber consists of a cylin- -d rical metal casing 1, the-bottom of which isenclosed by a-"di'sc 2,,' which is connected to the casing 'wallby solder- 'ing or-welding so;as-to m"ake' a gas-tight seal. The upper end of the casing is-el'osed by a threaded ring ,3 having gear teeth 4 onits exterior and thetop of the ring has plated'thereonamickel diaphragm S 'which constitutes the-window Qf-theeha'nib'er. "After the parts-have been assembled solder-"is applied between i the 3 lower part of the ring 3 and the casing 1 so that the chamber is completely sealed,themiddle of"thedisc' 2coinprising a glassto-metal seal -at- 6. fAt-the middle of the glass portion 6 is arod-shaped electrode-7 to 'which is atta'ched" oneplate 8 of theionization chamber the plate lzieingformed of thin sheet metal corrugated lengthwise ="to increase its stiffness. Atea'ch side ofthe plate-8areiurtherplates -'-9 which are-joined'to ailan'ge' It) on theflinterior of the casing- 1" and are thus in -'1 netal-lic connection therewith. The plates may converge towards one anotheras shown in Figure l as the-field strehg'th'declines at places more remote from the radio-active source. 'Beneaththe glass '6 and surroundiug the central electrode isametal ring -"11 which constitutes the guardring of'the chamber and -to which contact is'made by a bif-iir'cated spring-contact 12. Between the armsof f-thisco'ntact there is arranged a spring pressed stud l3-'which forms'the-connection tofthe central plate electrode 8. The chamber is supported on 'a' large helicalspring l'4 which contacts with'the base of the chamber and formsaconnection thereto. [The chamber may be' rotated about itsj longitudinalaxis by means Jotthe gear 4 which iserigagedby a pinionin thesame way as in Figure 3 wherefa pinionitllis shown and 'described later. The charnb'er jis fill'ed-with'a suitab ie gas,

say, amixture of argon and carbon dioxide, hndt'riis is V througha smallpipe 15,21 'similar pipe 16 "being pr ed' through which the [displaced air can pass. "fWhfenthe chamber has been; properly filled with the gas the ends of both pipes'are sealed by soldering. {The pressure in the chamber 'is slightly above atmospheric pressureijust enough'to cause a slight bulgejo'n th diaphragm s. It will be seen from Figure l that-the parts -described ai'e supported in acasing "17 and a cover, not shown in Figure 1, is provided which is clamped to this casing by bolts passing through the holes 18, Figure 2, members associated with the cover being arranged to press resiliently on the top of the chamber to hold it firmly in position and in close electrical contact with the spring 14. The arrangement will be better understood from the description of Figure 3 which is given later.

The radiation gauge is arranged to measure the mass of a loose tobacco filler in a cigarette making machine as shown in Figure 4. With earlier constructions of gauges for this purpose certain inaccuracies occurred due to the accumulation of dust either on the ionization chamber or on the radio-active source and the removal of this required a good deal of apparatus and was not easy to do. To overcome the difiiculties due to dust the trough along which the loose filler passes is arranged in the present instance to lie across the circular top of the chamber, i.e. the nickel diaphragm 5, as shown in Figure 4, and the paper runs across the diaphragm in contact therewith and sweeps away any dust by its movement. In order to do this, the chamber diaphragm is arranged slightly above the normal level of the bottom of the trough, but insulated from any metallic parts thereof by plates 35. As shown in Figure 4, the paper web P lies on top of the chamber 1 with the tobacco T on the paper and confined laterally by guides 19. Further description of Figure 4 is deferred for the moment.

Referrlng now to Figure 3, this view, as previously stated, shows a particular kind of housing for the chamber but it will be readily understood that the top of the housing can be of any shape to suit the use of the chamber. The mounting of the chamber is the same as in Figure 1 and needs no further description but the gear 4 is shown engaging teeth on a pinion 20 which can be rotated on a pin 21 by a tommy bar so as to rotate the chamber round its longitudinal axis, the chamber being supported meanwhile by the spring 14 which presses the chamber top against an insulating ring 23 which is part of the devices shown at the top of Figure 3 and which form no part of the present invention.

If, for any reason, it becomes necessary to remove the ionization chamber it is necessary to shield the source and for this purpose there is provided a hinged flap 32 which is under the influence of springs 33, and springs up to the chain-line position, Figure 3, to cover the aperture which would be left if the chamber and the base of the device, which is marked 34 and equivalent to the base 17 of Figure '1, were removed. This flap may be made of a transparent plastic material.

Referring again to Figure 4, it will be seen that the top of the chamber is pressed against stationary parts 35 so that the chamber is held in much the same manner as the chamber of Figure 3. The guides 19 control the tobacco filler laterally and the filler T is carried on the paper P and the edges of the paper are turned up as shown to hinder escape of filler or dust. Any dust which does reach the top of the chamber is swept away by the moving web but if desired suction may be exerted in the spaces 35A through apertures 36, to ensure that there is no dust deposit on the chamber. The ray source 29 is held as shown as near to the top surfaces of the guides 19 as possible. The source is fixed to a bar 40 slidable in a guide (not shown). If it is desired to remove the ionization chamber of Figure 4, the source is first moved back on its slide and any rays emitted are shielded by the bed of the cigarette machine which is a massive iron casting and a key operated lock may be used to fix the source in this safe position.

As previously remarked the sensitivity of a chamber may be adjusted by rotating the chamber. When the plates 9 of a chamber lie parallel to the tobacco filler, tlte effective aperture of the chamber is at a maximum.

When they are at right-angles to the filler the aperture is at the minimum. Thus rotation of the chamber afiords a very delicate means of adjusting the sensitivity of the chamber and in this way manufacture is expedited, since the accuracy of operation. can be ensured by rotation of the chambers.

What I claim as my invention and desire to secure by Letters Patent is:

1. A11 ionization chamber for a radiation gauge for measuring a moving tobacco filler including a radioactive source, said chamber having a window and con taining platelike electrodes so disposed that they lie in planes transverse to the plane of the window, and means for rotating the chamber whereby the electrode plates may be disposed in different angular relationships to the radio-active source of the gauge, thus presenting in combination with the tobacco filler passing between the source and the chamber differing areas of chamber to the rays emitted from the source.

2. An ionization chamber as claimed in claim 1 wherein the chamber is of cylindrical shape and the window is at an end of the cylinder.

3. An ionization chamber as claimed in claim 1 where in the planes of the electrodes are substantially normal to the plane of the window and cross-sections of the electrodes parallel to the plane of the window and in the same plane are parallel to one another.

4. An ionization chamber as claimed in claim 2 wherein the planes of the electrodes are substantially normal to the plane of the window and cross-sections of the electrodes parallel to the plane of the window and in the same plane are parallel to one another.

5. An ionization chamber as claimed in claim 1 adapted for the measurement of a tobacco filler carried on a moving web, and comprising means supporting said chamber adjacent said web with the window of the chamber in contact with said web.

References Cited in the file of this patent UNITED STATES PATENTS 2,397,073 Hare Mar. 19, 1946 2,465,821 Smoluchowski Mar. 29, 1949 2,586,303 Clarke Feb. 14, 1952 2,675,482 Burnton Apr. 13, 1954 2,715,195 Friedman Aug. 9, 1955 2,800,131 Malins July 23, 1957 2,812,464 Pepinsky Nov. 5, 1957 

1. AN IONIZATION CHAMBER FOR A RADIATION GAUGE FOR MEASURING A MOVING TOBACCO FILLER INCLUDING A RADIOACTIVE SOURCE, AND CHAMBER HAVING A WINDOW AND CONTAINING PLATELIKE ELECTRODES SO DISPOSED THAT THEY LIE IN PLANES TRANSVERSE TO THE PLANE OF THE WINDOW, AND MEANS FOR ROTATING THE CHAMBER WHEREBY THE ELECTRODE PLATES MAY BE DISPOSED IN DIFFERENT ANGULAR RELATIONSHIPS TO THE RADIO-ACTIVE SOURCE OF THE GAUGE, THUS PRESENTING IN COMBINATION WITH THE TOBACCO FILLER PASSING BETWEEN THE SOURCE AND THE CHAMBER DIFFERING AREAS OF CHAMBER TO THE RAYS EMITTED FROM THE SOURCE. 